FPGA (Field Programmable Gate Array) is a semiconductor device that allows users to arbitrarily determine (programming) the positioning of pins, an I/O signal allocated to each pin, a circuit structure, etc.
In general, to a power supply input unit to a semiconductor device, a decoupling capacitor (or referred to as a “bypass capacitor”) is mounted for the purpose of suppressing power supply noise generated from the semiconductor device or radiation electromagnetic noise (EMI) accompanied by the power supply noise. Advantages of the decoupling capacitor are confirmed generally by the use of a printed circuit board simulation.
A method for designing a mounting circuit of a decoupling capacitor when the decoupling capacitor is placed on an integrated circuit (IC) to be mounted is described in, for example, Japanese Laid-Open Patent Publication No. 2004-258869
However, in semiconductor devices, such as a high-performance FPGA, in which circuit operation is bulky, complicated, and arbitrary, it is dramatically difficult to estimate a suitable decoupling capacitor mounting manner. In a substrate on which such a semiconductor device is mounted, a guard band needs to be assumed because modeling and extraction of an operation pattern are extremely difficult. More specifically, in order to maintain design quality for preventing troubles, a decoupling capacitor is excessively mounted. Thus, a substrate manufacturing cost increases, and moreover manufacturability deteriorates.